1. Field of the Invention
The present invention relates to a hybrid module comprising circuitry constructed by integrating passive components, such as multilayer ceramic capacitors, and active components, such as semiconductor devices, on its substrate on which circuit patterns are formed.
2. Description of the Related Art
Conventional hybrid modules which has heat-generating components, such as field-effect transistors (FETs) and power semiconductor devices, on their substrate are known, including one which has a structure described below.
The hybrid module has chip-form electronic components, such as multilayer ceramic capacitors, and a heat-generating circuit component, such as a semiconductor device, including FETs, on the top surface of its substrate. The substrate is an aluminum-nitride-based ceramic substrate of good thermal conductivity. The chip-form electronic components are soldered to a land on the substrate. The circuit component is bonded to a land through solder bumps. Terminal electrodes of the hybrid module are formed on the sides of the substrate.
The hybrid module is mounted on a mother circuit board with its bottom, on which the circuit component is not formed, being opposed to the mother circuit board. When mounted, the terminal electrodes of the hybrid module are soldered to circuit patterns formed on the mother circuit board. An electrically conductive film formed on the mother circuit board is positioned between the substrate and mother circuit board. The electrically conductive film is made of material having good thermal conductivity so that heat generated in the hybrid module is efficiently transferred to the mother circuit board. In the hybrid module, heat generated by the components mounted on the substrate is transferred through the conductive film to the mother circuit board and radiated.
Thermal transfer in this hybrid module is inefficient because heat generated in the circuit component is transferred to the substrate through the solder bump of the circuit component, then to the mother circuit board through the conductive film. In addition, aluminum-nitride-based ceramics are expensive and uneconomical compared to common alumina-based substrate materials.